Objective-C Method Signatures. Are they inconsistant?

Question

Hey, I'm a newbie to Objective-C, but please help me out here.

What I'm seeing is that Method signatures in Objective-C that take multiple parameters seem inconsistent.

Example:

- (void) sendEmail: (NSString *) toStr
         subject:(NSString *) subjectStr
         body:(NSString *) bodyStr;

Ok, so here we have 3 "parameters" (at least that's what I'm used to calling them), but 2 of them have "external" names (subject, body) but the first one doesn't!!!!! Isn't there something wrong with that from a consistancy/style point of view??

When we call this method we do it like do it like :

[emailObj sendEmail:@"[email protected]" subject:@"testSub" body:@"this is a test"]

(hopefully I did that right, remember I'm a newbie)

So the subject and the body are clearly marked in the call, but not the "to" address? Seems really wacked to me. Why is that first parameter getting special treatment?

Answer 1

I would say that if you're confused about what a method does, then it's probably not named as well as it could've been.

Given the selector above, I would expect the 3 parameters to be some sort of email object, a subject, and a body. Since, however, the first parameter is not an "Email" object but rather the recipient of an email, I would probably rename this method to be:

- (void) sendEmailToRecipient:(NSString *)recipient subject:(NSString *)subject body:(NSString *)body;

Answer 2

In most cases, methods like this are normally named so that the lack of a name on the first parameter makes sense. In this case, I would expect something like sendEmailTo.

Answer 3

I guess you thought that in the method declaration

-(void) A:(NSObject*)a B:(NSObject*)b C:(NSObject*)c

A is the method name, B and C are the names of parameters.

In Objective-C, the totality A:B:C: is the method name (more technically, called the selector) and used as a unit when you call a method by name. For example,

 if([obj respondsToSelector:@selector(A:B:C:)]){
     ...
 }

checks if obj responds to A:B:C:. But [obj respondsToSelector:@selector(A:)] will be NO in this case.

So, you should really think of the totality of A:B:C: as the method name, and A is the name of the first parameter.

Note also that you can't call A:B:C: as A:C:B:, either.